This invention relates to injection devices.
After any injection, the syringe with its needle is thrown away into a guarded enclosure, for obvious safety reasons. But removing it from a re-usable device that first fires the syringe forwards to make the needle penetrate, then pushes the syringe piston forwards to eject the dose, and which finally withdraws the syringe and needle, can itself be hazardous and time-consuming.
One answer is to discard everything, but such injection devices are complex and expensive. That is not therefore a realistic option.
However, by making the device in two parts, one being a re-usable firing mechanism with a plunger that can be released to spring forwards, and the other being a housing and guide for the syringe to which the firing mechanism can be temporarily attached, it becomes possible to contemplate throwing away this other part (still containing a syringe)
It is also useful to be able to tell at a glance whether a device has been used or not, and to have some safety measure that will positively prevent projection of the needle both before and after use.
It is the aim of this invention to provide such a device.
According to one aspect of the present invention there is provided an injection device comprising a barrel, a syringe carrier within the barrel axially movable between a rearward position, in which the needle of a syringe carried thereby is retracted within the forward end of the barrel, and a forward position, in which the needle projects from the forward end of the barrel, spring means urging the syringe carrier towards the rearward position, and a connector with limited freedom of axial movement at the rear end of the barrel for attachment of a firing device whose firing member, when released, acts on the piston in the syringe to urge the syringe forwards and then to eject a dose, wherein at least one of the connector and the syringe carrier is initially held rigid with the barrel by a removable locking element inserted laterally through the barrel, wherein on removal of the locking element, the connector and the syringe carrier assume positions, when the barrel is held against the skin by the firing device being pressed forwards, for the carrier and its syringe to be propelled forwards on actuation of the firing device, and wherein the syringe carrier reverts under the influence of the spring means to a rearward position after removal of the injection device from the skin.
Thus the device is manifestly in a non-usable condition as long as the locking element is in place. If it has been removed, it signifies that the device has been used and should be discarded. It is of course not just a visual signal; it is primarily a physical barrier to operation.
In order to ensure that the locking element cannot be replaced after use, and thus give the impression of a fresh injection device, it will preferably be arranged that either or both the connector and the syringe carrier finish at respective positions where their detents that were originally engaged by the locking element are no longer in registry with the aperture in the barrel through which the locking element was entered. The connector may have a snap engagement with a detent internal of the barrel to capture it in its after use position, while the spring means can urge the carrier to the rear of its locked position.
Preferably the spring means will be partially energised in the initial locked position, so that when the locking element is removed, the spring means will urge the syringe carrier rearwardly, bringing the tip of the needle further back into the barrel from a nearly projecting position which enables the cap to be removed. At the same time, the carrier may act on the connector to push that rearwardly, although not so far that it is captured in its ultimate after use position. Conveniently, a snap engagement element on the connector is rendered inoperative before firing of the device by interengagement of the syringe carrier and the connector, said element in that inoperative state forming a stop that limits rearward movement of the connector.
After injection, the spring means will act through the carrier, the syringe and the firing member to cause the reversion of the connector to its rearward, captive position, the axial relationship between the syringe carrier and the connector having changed and removed the interengagement that rendered the snap engagement element inoperative and limited the rearward movement before firing.
Conveniently, the attachment of the firing device to the connector is by mating screw threads, the connector being restrained against rotation with respect to the barrel.
The connector may be a stepped tube, the smaller diameter portion at the rear end providing a socket to receive the firing device, the internal forward facing shoulder formed by the step providing an abutment for the rear end of the syringe carrier, and the external, rearward facing shoulder formed by the step providing an abutment for engagement with a locking ring, fitted to the rear end of the barrel, when the connector is at its after use position.
The syringe carrier may have its limit of forward movement defined by an abutment internal of the barrel. This can be provided by the rear end of guide means for keeping the syringe carrier co-axial with the barrel, and against which a flange at the rear end of the syringe carrier will abut. The flange may also provide the detent in which the locking element engages.
The spring means is conveniently a helical spring surrounding a needle unit to engage the forward end of the syringe carrier and reacting against an abutment within the forward end of the barrel.
Preferably, the forward end of the barrel is equipped internally with barbs which point towards the mouth. They will allow projection of the needle and removal of the needle cap, but make it virtually impossible to poke a finger in and contact the retracted needle.
The roots of the barbs conveniently provide the abutment for the spring.
Such an injection device is primarily intended for use with a syringe containing a two component dose, these components having to be mixed immediately before injection. One component is a liquid (which may simply be water) already within the syringe, while the other component is a powder, to be dispersed in or made into a solution with the liquid.
A further aim of this invention is to ease the mixing process, and the disposal of the container of the second component along with the used syringe.
According to another aspect of the present invention there is provided an adaptor for use in preparation of a syringe dose, the syringe initially containing a liquid, being without its needle assembly, and having a piston to which a rod can be temporarily attached, the dose to be administered being a mixture of the liquid and a substance loosely contained in a sealed vial with a membrane over its neck, the adaptor comprising a cup member with a centrally apertured base, the cup being adapted to fit closely over the neck of the vial and having a central hollow spigot upstanding from the base that will pierce the membrane of the vial when the cap is fitted to the vial, and a formation on the outside of the base adapted to attach to the rear end of an injection device, which for use has a firing device fitted to that rear end, the formation having a recess communicating with the central aperture and shaped closely to receive the neck of a syringe, wherein the adaptor enables (when the vial and syringe are fitted to said cup and said recess respectively) injection of the liquid through the aperture and said spigot into the vial, to mix with said substance, and subsequently the withdrawal of the mixture back into the syringe, which is then transferable to the injection device to co-operate with its needle assembly, and wherein, after use of the injection device, the firing device is replaceable by the adaptor with the vial still attached.
Said formation may be a second cup, back-to-back and having a common base with the first cup, and a central spigot formed with said recess, the second cup fitting over the rear end of the injection device. Alternatively, the formation may include an externally screw threaded plug that screws into a connector socket to which the firing device can fit.
While the injection is performed the adaptor and empty vial combination is laid aside, but after the injection the combination is fitted to the injector device and, when that is disposed of, so is the adaptor and vial.